1. Field of the Invention
The present invention relates to a process for producing a foamed resin article and the like, particularly to a process for producing a foamed resin article having fine cells in a high cell density and the like.
2. Description of the Related Art
In recent years, a supercritical foaming technique wherein a foamed resin article having fine cells in a high cell density is produced by using an inert substance (carbon dioxide, nitrogen and the like) in a supercritical state has been developed [see, for example, Material and Manufacturing Process, 4 (2), 253-262 (1989) and U.S. Pat. No. 5,160,674]. Development of techniques by which higher cell densities can be achieved is still required, however.
The object of the present invention is to provide a process for producing a foamed resin article having fine cells in a higher cell density, and the like.
The present inventors have studied intensively on a process for producing a foamed resin article having fine cells in a higher cell density, and as a result, have found a process for producing a foamed resin article comprising two steps using a specific resin material can attain the above object and have accomplished the present invention.
That is, the present invention provides:
1. a process for producing a foamed resin article, the process comprising: a step (the first step) of impregnating any one crystalline thermoplastic resin or resin composition containing, as an elementary ingredient, a crystalline thermoplastic resin selected from ones listed below, under an elevated pressure which is not lower than the critical pressure of a substance with which the selected crystalline thermoplastic resin or resin composition is to be impregnated, with a fluid of the substance, and a step (the second step) of releasing the resin or resin composition impregnated with the substance from the foregoing pressurized condition in a period of less than 10 seconds. (Hereinafter, it may sometimes be referred to as the process of the present invention.) (Crystalline Thermoplastic Resin or Resin Composition Containing, as an Elementary Ingredient, a Crystalline Thermoplastic Resin)
(a) A polypropylene resin which is a crystalline thermoplastic resin
(b) A resin composition comprising not less than 50% by weight of a polypropylene resin which is a crystalline thermoplastic resin, as an elementary ingredient
(c) A resin composition comprising 60 to 90 parts by weight of a crystalline thermoplastic resin as an elementary ingredient and 10 to 40 parts by weight of a non-crystalline thermoplastic resin
(d) A crystalline thermoplastic resin or a crystalline thermoplastic resin composition wherein an endothermic curve obtained by measurement at a rate of heating of 10xc2x0 C./min using a differential scanning calorimeter (DSC) has at least one endothermic peak and wherein when taking the highest peak point among the at least one endothermic peak as A, taking the point appearing on the higher temperature side at which the minimum endothermic heat value is given as F, taking the point at which a straight line (a base line) which passes through the point F and is parallel to the temperature axis intersects a perpendicular dropped from the point A to the temperature axis as B, taking the point which internally divides the segment AB in the perpendicular into 9:1 as C, taking the point at which a straight line which passes through the point C and is parallel to the temperature axis intersects the endothermic curve at the lowest temperature as D, and taking the point at which the line CD intersects the endothermic curve at the highest temperature as E, a difference in temperature indicated by the length of the segment DE is 20xc2x0 C. or more.
2. the process for producing a foamed resin article according to the above 1, wherein the release from the pressurized condition in the second step is conducted in a period of 3 seconds or shorter.
3. the process for producing a foamed resin article according to the above 1, wherein the second step is conducted at a lower temperature than a temperature at which the first step is conducted.
4. the process for producing a foamed resin article according to the above 1, wherein the release from the pressurized condition in the second step is conducted at a lower temperature than a melting point of the resin or resin composition used.
5. the process for producing a foamed resin article according to the above 1, wherein the impregnation in the first step is conducted under the pressurized conditions of at a temperature of 300xc2x0 C. or lower, in a period of 5 hours or shorter and at a pressure of 10 MPa or higher.
6. the process for producing a foamed resin article according to the above 1, wherein the impregnation in the first step is conducted under the pressurized conditions of at a temperature in the range of 60 to 230xc2x0 C., in a period of 3 hours or shorter and at a pressure in the range of 10 to 50 MPa.
7. the process for producing a foamed resin article according to the above 1, wherein the crystalline thermoplastic resin is a polypropylene resin, which is a crystalline thermoplastic resin. (Hereinafter, it may sometimes be referred to as the process A of the present invention.)
8. the process for producing a foamed resin article according to the above 1, wherein the resin composition is a resin composition comprising not less than 50% by weight of a polypropylene resin which is a crystalline thermoplastic resin, as an elementary ingredient. (Hereinafter, it may sometimes be referred to as the process Axe2x80x2 of the present invention.)
9. the process for producing a foamed resin article according to the above 1, wherein the resin composition is a resin composition comprising 60 to 90 parts by weight of a crystalline thermoplastic resin as an elementary ingredient and 10 to 40 parts by weight of a non-crystalline thermoplastic resin. (Hereinafter, it may sometimes be referred to as the process B of the present invention.)
10. the process for producing a foamed resin article according to the above 9, wherein the resin composition comprises a crystal phase and a non-crystal phase and the size of the non-crystal phase is 10 to 200 nm.
11. the process for producing a foamed resin article according to the above 1, wherein the crystalline thermoplastic resin or the resin composition is a crystalline thermoplastic resin or a crystalline thermoplastic resin composition wherein an endothermic curve obtained by measurement at a rate of heating of 10xc2x0 C./min using a differential scanning calorimeter (DSC) has at least one endothermic peak and wherein when taking the highest peak point among the at least one endothermic peak as A, taking the point appearing on the higher temperature side at which the minimum endothermic heat value is given as F, taking the point at which a straight line (a base line) which passes through the point F and is parallel to the temperature axis intersects a perpendicular dropped from the point A to the temperature axis as B, taking the point which internally divides the segment AB in the perpendicular into 9:1 as C, taking the point at which a straight line which passes through the point C and is parallel to the temperature axis intersects the endothermic curve at the lowest temperature as D, and taking the point at which the line CD intersects the endothermic curve at the highest temperature as E, a difference in temperature indicated by the length of the segment DE is 20xc2x0 C. or more. (Hereinafter, it may sometimes be referred to as the process C of the present invention.)
12. A foamed resin article produced by the process of the above 1. (Hereinafter, it may sometimes be referred to as the foamed resin article of the present invention.)
13. A foamed resin article characterized by being formed of a polypropylene resin which is a crystalline thermoplastic resin, or a resin composition comprising not less than 50% by weight of a polypropylene resin which is a crystalline thermoplastic resin, and by having an average cell density of not less than 1011 cells per cubic centimeter (cm3) of said resin or said resin composition. (Hereinafter, it may sometimes be referred to as the foamed resin article A of the present invention.)
14. The foamed resin article according to the above 13, wherein an average cell diameter is not greater than 2 xcexcm.
15. A foamed resin article characterized by being formed of a resin composition comprising 60 to 90 parts by weight of a crystalline thermoplastic resin as an elementary ingredient and 10 to 40 parts by weight of a non-crystalline thermoplastic resin, and by having an average cell density of not less than 1011 cells per cubic centimeter (cm3) of said resin or said resin composition. (Hereinafter, it may sometimes be referred to as the foamed resin article B of the present invention.)
16. The foamed resin article according to the above 15, wherein the non-crystalline thermoplastic resin is a polyolefin-based elastomer.
17. The foamed resin article according to the above 16, wherein the polyolefin-based elastomer is a hydrogenated styrene/butadiene copolymer or a propylene/butene copolymer.
18. A foamed resin article characterized by being formed of a crystalline thermoplastic resin or crystalline thermoplastic resin composition wherein an endothermic curve obtained by measurement at a rate of heating of 10xc2x0 C./min using a differential scanning calorimeter (DSC) has at least one endothermic peak and wherein when taking the highest peak point among the at least one endothermic peak as A, taking the point appearing on the higher temperature side at which the minimum endothermic heat value is given as F, taking the point at which a straight line (a base line) which passes through the point F and is parallel to the temperature axis intersects a perpendicular dropped from the point A to the temperature axis as B, taking the point which internally divides the segment AB in the perpendicular into 9:1 as C, taking the point at which a straight line which passes through the point C and is parallel to the temperature axis intersects the endothermic curve at the lowest temperature as D, and taking the point at which the line CD intersects the endothermic curve at the highest temperature as E, a difference in temperature indicated by the length of the segment DE is 20xc2x0 C. or more, and by having an average cell diameter of not greater than 10 xcexcm and an expansion ratio of not less than twice and not more than 40 times. (Hereinafter, it may sometimes be referred to as the foamed resin article C of the present invention.)
According to the foregoing process, a foamed resin article having fine cells in a cell density higher than that achieved by foaming resin materials other than the above-mentioned crystalline thermoplastic resin or resin composition comprising, as an essential ingredient, a crystalline thermoplastic resin (henceforth, the both may be referred to as xe2x80x9cthe present resin materialxe2x80x9d).
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.